Autofocus apparatus having a flash synchronized to an autofocus sampling time

ABSTRACT

The autofocus apparatus determines a focus position according to a result of sampling an AF evaluated value and drives a lens system to the focus position. This autofocus apparatus further performs a flash in synchronism with a sampling timing of an AF evaluated value.

FIELD OF THE INVENTION

The present invention relates to an autofocus apparatus. Moreparticularly, this invention relates to an autofocus apparatus for adigital camera or a digital video camera.

BACKGROUND OF THE INVENTION

Various systems have conventionally been proposed for the autofocusapparatus. For example, in silver-salt cameras of single-lens reflextype, autofocusing (AF) that uses the phase difference detection methodhas been utilized in a many models.

In the AF system using the phase difference detection method the outputsfrom an AF sensor and hence the distance between two images aredifferent according to a status of proper focus, a status offorward-offset focus, and a status of backward-offset focus. Therefore,the lens is driven to obtain proper focus in such a way that thedistance between the images becomes equal to a distance at the properfocus. Amount of movement of the lens, namely an amount of movement ofthe image surface is then calculated from the distance between the twoimages.

When the brightness of the object has low contrast then in this phasedifference detection method light is flashed from an electronic flashdevice built into the camera. Phase different with respect to the objectis detected based on the light reflected from the object. Whiledetecting the phase difference, proper focus can be obtained with onlyone output from the sensor, and flash can be used only once under theconditions of the low brightness and low contrast of the object.

On the contrary, digital still cameras or digital video cameras use asystem which is called an exploratory AF system. In this system, thelens position at which a high-frequency component of a brightness signalobtained by an image pickup device such as a CCD becomes maximum isdetermined as a focus position.

For example, an autofocus apparatus that uses the exploratory AF systemis disclosed in Japanese Patent Laid-Open Publication No. HEI 5-268505.The autofocus apparatus disclosed in this publication comprises a flashfor flashing light onto an object, a light receiver for receiving alight reflected from the object, a flash-light quantity changing unitfor varying a light quantity of the flash. Further, an AF computing unitis provided for AF computing. Further, a lens is provided foraccumulating the light reflected from the object and a lens driving unitis provided for driving the lens. A control section is provided forcontrolling each of the above-mentioned components. The control sectioncontrols in such a way that the AF computing unit does not getsaturated.

The conventional technology described above gives good results in a casewhere AF is slow in a direction of increasing the quantity of the lightto be flashed by successively increasing a driving time of theelectronic flash device so as to match the change in the distance whilesuccessively driving a focal lens to a further position. However,because an AF evaluated value is computed by using a brightness signalthis value becomes larger as the brightness signal becomes larger. Thisfact disadvantageously causes a focus position of the focal lens not tobe a peak of a sampled AF evaluated value.

SUMMARY OF THE INVENTION

In light of the problems described above, it is an object of the presentinvention to provide an autofocus apparatus enabling a high-speed andhigh-precision focusing operation even when an object has a lowbrightness, low reflection factor, and low contrast.

In an autofocus apparatus according to this invention, a flash isperformed in synchronism with a sampling timing of an AY evaluatedvalue. Therefore, high-speed and high-precision focusing can beperformed even when the object has low brightness, low reflectionfactor, and low contrast.

Other objects and features of this invention will become apparent fromthe following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a digital camera according to theinvention;

FIG. 2 is a view showing an example of configuration of the electronicflash device in FIG. 1;

FIG. 3 is a view showing an example of concrete configuration of IPP inFIG. 1:

FIG. 4 is a flow chart for explaining an autofocus operation accordingto the preferred embodiment of the invention;

FIG. 5 is a flow chart for explaining a setting operation for performingthe autofocus operation according to the preferred embodiment of theinvention;

FIG. 6 is a view for explaining a set value according to the preferredembodiment of the invention;

FIG. 7 is a view showing a ZF table used when a focus position withrespect to a zoom position is adjusted in the preferred embodiment ofthe invention;

FIG. 8 is a view showing the ZF table in FIG. 7 in graphical form;

FIG. 9 is a circuit diagram showing drivers of the zoom pulse motor aswell as of a focus pulse motor according to the preferred embodiment ofthe invention;

FIG. 10 is a view showing a truth table of the pulse motor driving IC inthe driver shown in FIG. 8;

FIGS. 11A to 11D are timing charts for explaining an operation example1;

FIG. 12 is a timing chart for explaining an operation example 3; and

FIG. 13 is a timing chart for explaining an operation example 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Detailed description is made hereinafter for the preferred embodimentsof an autofocus apparatus according to the present invention withreference to the attached drawings.

FIG. 1 is a block diagram showing a digital camera with an autofocusapparatus according to a preferred embodiment of the invention appliedtherein. In this figure, the reference numeral 100 indicates a digitalcamera. This digital camera 100 comprises a lens system 101, amechanical system 102 including a diaphragm and a filter or the like, aCCD (Charge-Coupled Device) 103, a CDS (Correlation Dual Sampling)circuit 104, an automatic gain control amplifier (AGC amplifier) 105, anA/D converter 106, an IPP (Image Pre-Processor) 107, a DCT (DiscreteCosine Transform) 108, a coder 109, an MCC (Memory Card Controller) 110,a DRAM 111, a PC card interface 112, a CPU 121, a display section 122,an operating section 123, an SG (control signal generating) section 126,an electronic flash device 127 for flashing a light under the control ofthe CPU 121, a buttery 128, a DC-DC converter 129, an EEPROM 130, afocus driver 131, a pulse motor 132, a zoom driver 133, a pulse motor134, and a motor driver 135. In addition, a detachable PC card 150 isconnected to the digital camera 100 via the PC card interface 112.

A lens unit comprises the lens system 101 and the mechanical system 102including a diaphragm and a filter or the like, and a mechanical shutterof the mechanical system 102 performs concurrent exposure in two fields.The lens system 101 is formed with, for example, a vari-focal lens, andcomprises a focus lens system 101 a and a zoom lens system 101 b.

The focus driver 131 drives the focus pulse motor 132 according to acontrol signal supplied from the CPU 121 to move the focus lens system101 a in the direction of the optical axis thereof. The zoom driver 133drives the zoom pulse motor 134 according to a control signal suppliedfrom the CPU 121 so as to move the zoom lens system 101 b in thedirection of the optical axis thereof. The motor driver 135 drives themechanical system 102 according to a control signal supplied from theCPU 121, to set, for example, an f-stop value of the aperture.

The CCD 103 converts a picture which is inputted via the lens unit to anelectric signal (analog image data). The CDS circuit 104 is a circuitwhich reduces noise of the CCD-type image pickup device.

The AGC amplifier 105 corrects a level of a signal which is subjected tocorrelation dual sampling in the CDS circuit 104. A gain of the AGCamplifier 105 is set by the setting-data (control voltage) in the AGCamplifier 105 by the CPU 121 via the D/A converter incorporated in theCPU 121. Furthermore, the A/D converter 106 converts analog image datafrom the CCD 103 which is inputted via the AGC amplifier 105 to digitalimage data. That is, an output signal from the CCD 103 is converted to adigital signal at an optimal sampling frequency (e.g., an integralmultiple of a sampling frequency of an NTSC signal) via the CDS circuit104 and the AGC amplifier 105 and by the A/D converter 106.

The IPP 107, the DCT 108, and the coder (Huffman Encoder/Decoder) 109comprise a digital signal processing section. This digital signalprocessing section divides the digital image data which is inputted fromthe A/D converter 106 into color difference (Cb, Cr) and brightness (Y)and does data processing for various purposes, correction or imagecompression/decompression with respect to this divided data.

Furthermore, the MCC 110 stores a compressed image therein once andrecords the data to the PC card 150 via the PC card interface 112 orreads data from the PC card 150.

The CPU 121 uses the RAM as a work area according to a program stored inthe ROM and also controls the entire operations of the digital cameraaccording to an instruction from the operating section 123 or accordingto an instruction through an operation by an external device such as aremote controller not shown herein. Concretely, the CPU 121 controlsoperations such as an image pickup operation, an autoexposure (AE)operation, an automatic white balance (AWB) adjustment operation, and anAF operation.

Power is inputted to a DC-DC converter 129 from the buttery 128 such asa NiCd battery, a nickel-metal hydride battery, or a lithium battery,and then the power is supplied to all the sections the digital camera100.

The display section 122 is realized by an LCD, an LED, or an EL. Thedisplay section 122 displays picked-up digital image data or recordedimage data which has been compressed or decompressed. The operatingsection 123 has buttons for performing operations of function selection,instruction for photographing, and other various settings from theoutside. Adjustment data or the like which is used when the CPU 121controls operations of a digital camera is written in the EEPROM 130.

The above mentioned digital camera 100 (to be precise the CPU 121) hasRecording mode for recording image data which is obtained byphotographing the object to the PC card 150, Displaying mode fordisplaying the image data which is recorded on the PC card 150, andMonitoring mode for directly displaying the picked-up image data on thedisplay section 122.

FIG. 2 is a view showing an example of configuration of the electronicflash device 127. The electronic flash device 127 comprises, as shown inthis figure, a charging circuit 201 for charging a main capacitor MCaccording to a charging signal from the CPU 121, the main capacitor MCto be charged by a voltage outputted from the charging circuit 201,partial pressure resistors R1 and R2 each for detecting a chargingvoltage to be charged to the main capacitor MC by the CPU 121, a flashtube Xe switched by an IGBT according to the charged voltage in the maincapacitor MC to perform a flash, the IGBT being ON/OFF by a gate drivingcircuit 202 to switch the flash tube Xe, and a gate driving circuit 202for turning ON/OFF the IGBT according to a flash timing signal from theCPU 121.

When a flash is to be performed, the CPU 121 sends a charge signal tothe charging circuit 201 so as to charge the main capacitor MC. Thecharged voltage in the main capacitor MC is detected in the CPU 121 viathe partial pressure resistors R1 and R2. The CPU 121 ends charging ofthe main capacitor MC when the charge reaches a specified voltage. TheCPU 121 then sends a flash timing signal to the gate driving circuit202. The gate driving circuit 202 makes the flash tube Xe flash via theIGBT in response to reception of the flash timing signal. With thisoperation, a light is flashed onto the object. That is, the flash tubeXe flashes light according to a flash timing signal from the CPU 121.

FIG. 3 is a view showing an example of concrete configuration of the IPP107. The IPP 107 comprises, as shown in FIG. 3, a color separatingsection 1071 for separating digital image data inputted from the A/Dconverter 106 to each color component of R•G•B, a signal interpolatingsection 1072 for interpolating between the separated image data ofR•G•B, a pedestal adjusting section 1073 for adjusting a black level ofeach image data of R•G•B, a white balance adjusting section 1074 foradjusting a white level of each image data of R and B, a digital gainadjusting section 1075 for correcting each image data of R•G•B with thegain set by the CPU 121, a gamma converting section 1076 forγ-converting each image data of R•G•B, a matrix section 1077 forseparating image data of R•G•B to a color difference signal (Cb, Cr) anda brightness signal (Y), and a video signal processing section 1078 forpreparing a video signal according to the color difference signal (Cb,Cr) and brightness signal (Y) to output the signal to the displaysection 122.

The IPP 107 also comprises a Y-computing section 1079 for detectingbrightness data (Y) of image data after being subjected to pedestaladjustment by the pedestal adjusting section 1073, a BPF 1080 forpassing therethrough only a specified frequency component of thebrightness data (Y) which is detected in the Y-computing section 1079,an AF evaluated value circuit 1081 for outputting an integrated value ofthe brightness data (Y) which is passed through the BPF 1080 to the CPU121 as an AF evaluated value, an AE evaluated value circuit 1082 foroutputting a digital count value corresponding to the brightness data(Y) detected in the Y-computing section 1079 to the CPU 121 as an AEevaluated value. Further, the IPP 107 comprises a Y-computing section1083 for detecting brightness data (Y) of each image data of R•G•B afterbeing subjected to white balance adjustment in the white balanceadjusting section 1074, an AWB evaluated value circuit 1084 for countingbrightness data (Y) for each color which is detected in the Y-computingsection 1083 and outputting the data to the CPU 121 as an AWB evaluatedvalue for each color, a CPU I/F 1085 as an interface with the CPU 121,and a DCT I/F 1086 as an interface with the DCT 108.

The AF control is described bellow. In the AF control, after a shutterspeed and a gain are set, a focus pulse motor 132 is driven according tospecified pulses during a 1Vd period. While the focus pulse motor 132 isdriving for specified pulses, a digital video signal obtained in the IPP107 is processed to obtain a brightness signal. High-frequencycomponents of this brightness signal are integrated to obtain an AFevaluated value, and the peak of this AF evaluated value is decided as afocus position.

In zoom control, the present position (distance) of the focus betweenthe set value “fp far calc” (Infinity) described later and the set value“fp near calc” (Close proximity; about 0.2 m) can be obtained from aratio. The focus position is driven, in association with zoom driving,to the position that becomes the same ratio with the above ratio from“fp far def” and “fp near def” at the zoom point so that an out-of-focuscaused by zooming of a vari-focal lens can be corrected.

The set values which are also the adjustment values for AF operationsare described bellow. FIG. 4 is a view for explaining the set values. Itis assumed that autofocusing is performed, as shown in FIG. 4, by usinga vari-focal lens with nine zoom steps (positions) from 00 to 08. Therange of photography is from Infinity to around 0.2 m, and is to around0.01 m only for a wide-angle shot.

In a table shown in FIG. 4, each of the zoom steps has six types of setvalue of “ccdaf drv data”, “fp far def”, “fp near def”, “fp far calc”,“fp near calc”, and “nml smp” correlated thereto respectively. Each ofthe set values in FIG. 4 is represented in hexadecimal notion.

Herein, the “ccdaf drv data” represents a driving rate (the number ofpulses) of a focus lens system for each sampling when an AF evaluatedvalue is sampled. The “fp far def ” represents a starting position forsampling an AF evaluated value in each zoom step and a difference from aposition of the number of pulses “fp inf def” generated for focusing asa reference has been inputted thereto as data.

The “fp near def” represents a sampling end position for an AF evaluatedvalue in each of the zoom steps and a difference from the position ofthe number of pulses “fp inf def” generated for focusing as a referencehas been inputted thereto as data. The “fp far calc” represents aninfinity position in each of the zoom steps and a difference from theposition of the number of pulses “fp inf def” generated for focusing, asa reference has been inputted thereto as data.

The “fp near calc” represents a position of 0.2 m in each of the zoomsteps and a difference from the position of the number of pulses “fp infdef” generated for focusing as a reference has been inputted thereto asdata. The “nml smp” represents the number of samplings for driving thefocus lens system to sample along the entire area where sampling of AFevaluated values is inevitably executed regardless of a sampling resultof AF evaluated values.

The “fp inf def” represents the number of pulses generated for focusingfrom the mechanical end in the infinity side of the focus to thestarting point of sampling an AF evaluated value of wide-angle.

Operation of this embodiment is explained bellow. FIG. 5 is a flow chartfor explaining a setting operation for performing the autofocusoperation. FIG. 6 is a flow chart for explaining the autofocusoperation.

In FIG. 6, each set value is described as follows: fp far init=thenumber of pulses generated for focusing (fp inf def)−an AF evaluatedvalue sampling starting position (fp far def [zoom]), fp near init=thenumber of pulses generated for focusing (fp inf def)+an AF evaluatedvalue sampling end position (fp near def [zoom]), fp home=(fp farinit)−(fp home def), and nml smp def=nml smp [zoom]. Herein, zoomrepresents a position in 9 zoom steps, and zoom=0 represents “wide”position, zoom=4 represents “mean” position, and zoom=8 represents“tele” position.

In the operation shown in FIG. 6, at first, zoom reset is executed bymatching a zoom position with the number of pulses for zoom driving, andthen focus reset is executed by matching a focus position with thenumber of pulses for focus driving. These zoom reset and focus reset areexecuted by driving each position to the mechanical end respectively.

A position after driving with the number of pulses more than that fordriving each position to the mechanical end is decided as a position ofa specified number of pulses. Herein, in a case of focusing, fp max=205pulses is shown at the mechanical end in the “near” side. Data for alast pulse output when driving the focus to the mechanical end is set onadjustment as fp home state. Next, the focus is set at a normal focalposition (around 2.5 m), and then zooming is executed.

Then, the operation shown in FIG. 5 is started. The operation mode shownin FIG. 5 is Autofocus mode. In the Autofocus mode, at first, AF initialsetting (ccdaf init set) is executed (step S1), and first release isoperated. In this process, a normal focal position (around 2.5 m) at theset zoom point is computed from an adjusted value, and the AF operationis performed. Then, setting of AE (ccdaf ae set) for AF is executed(step S2).

In step S3, the focus is driven to the home position HP (fp home). Instep S4, the focus is driven to the initial position INIT (fp far init).As described above, by driving the focus from the home position HP tothe initial position INIT, backlash (fp b lash=8 (pulses)) can beremoved.

The processing is then shifted to step S5. Driving of the focus at thetime of sampling an AF evaluated value is executed in synchronism with avertical synchronizing signal Vd. In this case, the focus is driven foran amount (ccdaf drv data) of a focus lens system for each sampling. Inthis process, driving of the focus is continued as far as the “near”position (until an AF evaluated value by nml smp is sampled, which is upto (ccdaf drv data)*(nml smp) as a driving rate of the focus) regardlessof any value (information such as a peak) of the AF evaluated values.This is within a normal range of a photographing distance (from Infinityto around 0.5 m).

Herein, a peak position and data for fluctuations in an AF evaluatedvalue or the like are computed from the AF evaluated value sampledwithin the normal range of a photographing distance, and it isdetermined whether or not a focus position exists within the normalrange of a photographing distance. Even when focusing is executed withina macro range of a photographing distance, the focus lens is driven to afocus position, after the focus is driven from the focus position to aposition where backlash is removed.

The processing is then shifted to step S6. In step S6, when a focusposition is within the normal range of photography then the sampling ofan AF evaluated value is stopped, and after the focus is driven from thefocus position to a position where backlash is removed the focus isagain driven to the focus position.

Furthermore, when the focus position is not within the normal range ofphotography, an AF evaluated value within the macro range of aphotographing distance (from around 0.5 m to around 0.2 m) is sampled(up to macro: fp near init). However, sampling of an AF evaluated valueis stopped when a peak is detected within the macro range of aphotographing distance.

The processing is then shifted to step S7. In step S7, the driving ofthe focus is turned OFF (fcsm off), and the processing ends.

A relation between a zoom position and a focus position is explained.FIG. 7 is a view showing a ZF (zoom-focus) table used for focus positionadjustment. FIG. 8 shows the ZF table in FIG. 7 in a graphical form.

The ZF table is used for adjusting a focus position to a zoom position.The ZF table shown in FIG. 7 shows three examples, No. 0, No. 1, and No.2. In any of the examples, nine positions between a Wide (W) end . . . aMean (M) . . . a Tele (T) end are allocated to two references ofInfinity and Close proximity (e.g., 20 cm). This ZF table contains thenumber of pulses ZP and an adjustment value (f (mm)) corresponding tothese nine positions. This ZF table is stored in a ROM or the like.

FIG. 8 shows Infinity reference A0-1 and Minimum range reference B0-1 asa graph of No. 0, Infinity reference A1-1 and Close proximity referenceB1-1 as a graph of No. 1, and Infinity reference A2-1 and Closeproximity reference B2-1 as a graph of No. 2. It is clear from thesegraphs that the number of pulses becomes smaller in the case of Closeproximity reference as compared to that in the case of Infinityreference.

The drivers are described here. FIG. 9 is a circuit diagram showing thedrivers of a zoom pulse motor 132 as well as of a focus pulse motor 134(focus driver 131 and zoom driver 133), and FIG. 10 is a view showing atruth table of a pulse motor driving IC. In FIG. 9, the focus driver 131and zoom driver 133 define a relation of input/output according to thetruth table shown in FIG. 10.

According to the truth table shown in FIG. 10, when an enable signal ineach of the circuits is “L” (LOW), there is no input (IN 1, 2) into thefocus driver 131 and zoom driver 133 shown in FIG. 9, and they are inthe standby mode with each output (OUT 1, 2, 3, and 4) is OFF. On theother hand, when the enable signal is “H” (HIGH), according to thelogical relation between the inputs IN 1 and IN 2, they drive and theoutputs OUT 1 to 4 becomes outputs for generating changes in two-phaseexcitation.

An AF operation along with a flash is explained below with reference toan operation example 1 to an operation example 6. The AF operation alongwith a flash is effective when the object has low brightness, lowreflection factor, and low contrast.

Operation example 1 is explained here with reference to FIGS. 11A to11D. FIGS. 11A to 11D are timing charts that explain the operationexample 1. FIG. 11A shows a vertical synchronizing signal (VD). FIG. 11Bshows a sampling timing of an AF evaluated value (image fetchingtiming). FIG. 11C shows a driving pulse (driving timing of the lenssystem 101) of the a pulse motor. FIG. 11D shows a timing at which theelectronic flash device 127 performs a flash.

The operation example 1 shows a case where a flash is performed insynchronism with a sampling timing of an AF evaluated value and thequantity of light of each flash is maintained at a constant value as faras possible.

At first, the CPU 121 drives the pulse motors (focus pulse motor 132,zoom pulse motor 134) at a timing shown in FIG. 11C to drive the lenssystem 101 (focus lens system 101 a, zoom lens system 101 b). Further,the CPU 121 fetches an image at the timing shown in FIG. 11B whiledriving the lens system 101 to compute an AF evaluated value in theabove mentioned method.

Then, the CPU 121 makes the flash tube Xe of the electronic flash device127 flash in synchronism with the timing shown in FIG. 11D, namely withthe sampling timing of an AF evaluated value during integration of CCDbefore the image is fetched. In this process, the CPU 121 controls alight quantity of the flash by the flash tube Xe according to a chargedvoltage in the main capacitor MC of the electronic flash device 127(Refer to FIG. 2) as well as to an ON time of the IGBT (flashing time)as described above. Then, the CPU 121 determines a focus positionaccording to the sampled AF evaluated value and drives the lens system101 to the focus position.

As described above, with the operation example 1, a flash is performedin synchronism with a sampling timing of an AF evaluated value in such away that the quantity of light of each flash is maintained constant asfar as possible. Accordingly, the same quantity of reflected light fromthe object can be received by the CCD 103 at the time of sampling ofeach AF evaluated value, which allows a focus position to be identifiedwith high precision even if the object has a low brightness, lowreflection factor, and low contrast.

An operation example 2 is explained here. The operation example 2 showsa case where sampling of an AF evaluated value is performed within awhere the flash reaches.

At first, the CPU 121 determines a maximum distance (e.g., 3 m) where aflash can reach. The maximum distance where the flash can reach isdetermined according to an F value of the lens system 101, sensitivityof the CCD 103, and a gain of the AGC amplifier 105 or the like.Further, a distance for photography (focus position) at each focaldistance (zoom position) can be detected or set according to the numberof pulses for driving a pulse motor.

The CPU 121 drives the lens system 101 from a minimum distance (whichmay be a shortest distance for photographing with a flash-lightadjusted) up to the above-mentioned reachable maximum distance to samplean AF evaluated value and also makes the flash tube Xe of the electronicflash device 127 flash in synchronism with a sampling timing of an AFevaluated value. In that process, the CPU 121 controls, same as to theoperation example 1, a quantity of light of the flash by the flash tubeXe according to a charged voltage in the main capacitor MC of theelectronic flash device 127 (Refer to FIG. 2) as well as to an ON timeof the IGBT (flashing time). Then, the CPU 121 determines a focusposition according to the sampled AF evaluated value and drives the lenssystem 101 to the focus position.

Furthermore, in the operation example 2, sampling of an AF evaluatedvalue and a flash are executed within a range where a flash can reach(within a photographable range), so that the areas where the AFevaluated values are sampled and the number of flashes can be reduced.This allows a time for executing an AF operation to be reduced as wellas power consumption to be decreased. Further, this operation allows thelight quantity per sampling of an AF evaluated value to be larger, sothat proper focus can be obtained even if the object has a lowreflection factor.

Operation example 3 is described here with reference to FIG. 12. FIG. 12is a timing chart for explaining the operation example 3, which shows aflashing timing. The operation example 3 shows a case where a flash isperformed for both the purposes of acquiring an AF evaluated value andthe purpose of reducing red-eye.

At first, the CPU 121 performs sampling of an AF evaluated value whiledriving the lens system 101, and makes the flash tube Xe of theelectronic flash device 127 flash in synchronism with the samplingtiming of an AF evaluated value during integration of the CCD before animage is fetched ( 1/60Hz). In that process, the CPU 121 controls thequantity of light of the flash from the flash tube Xe according to acharged voltage in the main capacitor MC of the electronic flash device127 (Refer to FIG. 2) as well as to an ON time of the IGBT (flashingtime).

Then, even flash is performed in synchronism with the sampling timing ofan AF evaluated value, when the flash does not reach a totalstrobe-light quantity as well as the number of flashing which have theeffect of reducing the red-eye effect, only flash is continuouslyperformed until the effect of reducing red-eye is attained.

Then, the CPU 121 computes a peak (focus position) according to thesampled AF evaluated value to drive the lens system 101 to the focusposition. After the step, if a charged voltage in the electronic flashdevice 127 (a charged voltage in the main capacitor MC) decreases, theCPU 121 charges the electronic flash device during the period until thenext flashing after the lens system 101 is driven to the focus position.

The CPU 121 performs a flash about 1 second after the flash which is insynchronism with initial sampling of an AF evaluated value and record animage. In a focus-lockable digital camera, when recording is operatedafter the time passes after locking of the focus, recording may beoperated after flashing for reduction of red-eye is performed as usual.

As described above, in the operation example 3, a flash is shared forboth the purposes of acquiring an AF evaluated value and the purpose ofreducing red-eye. Therefore, the time for executing an AF operation andpower consumption can be reduced. Further, an uneasiness caused due to aplurality flashes is also eliminated.

Operation example 4 is explained here with reference to FIG. 13. FIG. 13is a timing chart for explaining the operation example 4, which shows aflashing timing. The operation example 4 shows a case where there aresteps of acquiring an AE evaluated value by pre-flashing, calculating alight quantity of a flash and a gain set value of the AGC amplifier 105according to the AE evaluated value, setting the calculated lightquantity and gain set value of the AGC amplifier 105, and performing aflash in synchronism with the sampling timing of an AF evaluated value.

At first, the CPU 121 performs pre-flashing from the electronic flashdevice 127 to acquire an AE evaluated value in order to compute astrobe-light quantity (exposure time) at the time of sampling an AFevaluated value as well as a gain value of the AGC amplifier 105. Thearea where AE evaluated values are acquired is the substantially same asthe area where AF evaluated value are sampled.

Then, the CPU 121 calculates a strobe-light quantity at the time ofsampling an AF evaluated value as well as a gain value of the AGCamplifier 105 according to the acquired AE evaluated value, and sets thegain value of the AGC amplifier 105.

Then, the CPU 121 performs sampling of an AF evaluated value whiledriving the lens system 101, and makes the flash tube Xe of theelectronic flash device 127 flash in synchronism with the samplingtiming of an AF evaluated value during integration of the CCD before animage is fetched ( 1/60Hz). Then, the CPU 121 computes a peak (focusposition) according to the sampled AF evaluated value to drive the lenssystem 101 up to the focus position.

The CPU 121 sets a gain value of the AGC amplifier 105 for flashing whenan image is recorded, and a flash is performed after about 1 second fromthe flash which is in synchronism with initial sampling of an AFevaluated value, and records an image.

As described above, with the operation example 4, there are steps ofacquiring an AE evaluated value by pre-flashing, calculating astrobe-light quantity and a gain set value of the AGC amplifier 105according to the AE evaluated value, setting the calculated strobe-lightquantity and gain set value of the AGC amplifier 105, and flashing insynchronism with the sampling timing of an AF evaluated value.Therefore, a probability of saturation of AF evaluated values which isdue to a position of the lens system 101 can be reduced.

Explanation of an operation example 5 will be described bellow. By theway, there is sometimes a case where flashing can not continuously bemade by the number of samplings of an AF evaluated value when the objectis in a distance or the object has low reflection factor. In theoperation example 5, then, a necessary number of samplings of an AFevaluated value and a strobe-light quantity that can be flashed at thetime of said sampling are computed, or a necessary strobe-light quantityfor sampling an AF evaluated value is calculated according to an AEevaluated value acquired by pre-flashing, and a strobe-light quantity orthe like is determined by comparing both results of calculation.

At first, the CPU 121 determines a range where the lens system 101(e.g., 0.5 to 3 m) can be driven concurrently with flashing according toan F value or the like in a set focal distance. Then, the CPU 121determines the number of samplings of an AF evaluated value fordetecting a peak (focus position) within the above mentioned range. TheCPU 121 computes a strobe-light quantity which can be flashed at onesampling of an AF evaluated value according to a charged voltage in theelectronic flash device and the number of samplings of AF evaluatedvalue. Then, the CPU 121 acquires an AE evaluated value by pre-flashingto determine a strobe-light quantity for sampling an AF evaluated value.The CPU 121 calculates a strobe-light quantity according to the acquiredAE evaluated value.

After the steps, the CPU 121 compares the strobe-light quantitycalculated according to a charged voltage in the electronic flash deviceas well as to the number of samplings of an AF evaluated value to thestrobe-light quantity calculated according to the AE evaluated valueacquired by pre-flashing. When the strobe-light quantity calculatedaccording to the AE evaluated value acquired by pre-flashing is largerthan the strobe-light quantity calculated according to the chargedvoltage in the electronic flash device as well as to the number ofsamplings of the AF evaluated value as a result of the comparison, theCPU 121 flashes a strobe light in synchronism with the sampling timingof an AF evaluated value in the strobe-light quantity calculatedaccording to the charged voltage in the electronic flash device as wellas to the number of samplings of the AF evaluated value. In thatprocess, it may be programmed to increase a gain of the AGC amplifier105.

When the strobe-light quantity calculated according to the AE evaluatedvalue by pre-flashing is larger than the strobe-light quantitycalculated according to the charged voltage in the electronic flashdevice as well as to the number of samplings of the AF evaluated value,the number of sampling of an AF evaluated value may be reduced and astrobe light may be flashed in the strobe-light quantity calculatedaccording to the AE evaluated value acquired by pre-flashing in place offlashing a strobe light in the strobe-light quantity calculatedaccording to the charged voltage in the electronic flash device as wellas to the number of samplings of the AF evaluated value.

As described above, with the operation example 5, there are steps ofcomparing a strobe-light quantity computed according to a chargedvoltage in the electronic flash device as well as to the number ofsamplings of an AF evaluated value to a strobe-light quantity calculatedaccording to the AE evaluated value acquired by pre-flashing; flashing astrobe light which is in synchronism with the sampling timing of an AFevaluated value, when a strobe-light quantity calculated computedaccording to the AE evaluated value acquired by pre-flashing is largerthan a strobe-light quantity calculated according to a charged voltagein the electronic flash device as well as to the number of samplings ofan AF evaluated value, in the strobe-light quantity calculated accordingto the charged voltage in the electronic flash device as well as to thenumber of samplings of the AF evaluated value; or reducing the number ofsamplings of an AF evaluated value, and flashing a strobe light in astrobe-light quantity calculated according to the AE evaluated valueacquired by pre-flashing. That is, a strobe-light quantity or the numberof samplings of an AF evaluated value are reduced as required, whichallows a strobe light for each sampling of an AF evaluated value to bemaintained constant. Also, this operation enhances a possibility ofobtaining proper focus even with an electronic flash device having alimited function.

Explanation of an operation example 6 will be described bellow. Theoperation example 6 shows a case where sampling of an AF evaluated valuewith flashing is not executed, when an AE evaluated value is notimproved even flashing.

At first, the CPU 121 acquires an AE evaluated value when pre-flashingis made to determine a strobe-light quantity for flashing in synchronismwith a sampling timing of an AF evaluated value. Then, the CPU 121acquires an AE evaluated value when flashing is not made. Then, the CPU121 compares an AE evaluated values which are with or without flashing.And it does not execute sampling of an AF evaluated value when theevaluated values are not different to each other. That is, when an AEevaluated value is found not to increase by flashing because a strobelight does not reach to the object which is located far from theelectronic flash device or the object has a low reflection factor.

As described above, with the operation example 6, when an AE evaluatedvalue is not improved even by flashing, it is considerable that a strobelight does not reach the object located far from the electronic flashdevice or the object has a low reflection factor, and because of that,it is difficult to detect a peak of an AF evaluated value even bysampling of the AF evaluated value with flashing. Therefore it ispossible to prevent a waste of power consumption as well as of time forexecution, by selecting not to sample an AF evaluated value withflashing.

Although a strobe light is used as an auxiliary light in the abovementioned embodiment, the present invention is not limited to the lightdescribed above, and it may use any auxiliary light such as a lamp and ahigh-brightness LED.

The present invention is not to be thus limited but are to be construedas embodying all modifications and alternative constructions that mayoccur to one skilled in the art which fairly fall within the basicteaching herein set forth.

With the present invention, in an apparatus for determining a focusposition by a result of sampling an AF evaluated value and driving afocus lens system to the focus position, a strobe light is flashed insynchronism with a sampling timing of an AF evaluated value, and aquantity of the light of each flash is maintained constant. Therefore ahigh-speed and high-precision focusing operation becomes possible evenwhen the object has low brightness, low reflection factor, and lowcontrast.

With the present invention, in the apparatus described above, a rangewhere an AF evaluated value is sampled is set to a range where a strobelight can reach. Therefore, it is possible to reduce time for executingan AF operation as well as power consumption.

With the present invention, in the apparatus described above, a flash isused to obtain an AF evaluated value as well as for reducing the red-eyeeffect. Therefore, it is possible to reduce time for executing an AFoperation as well as power consumption, and also to eliminate theuneasiness which is due to multi-flashing.

With the present invention, in the apparatus described above, a lightquantity of a flash is determined in synchronism with a sampling timingof an AF evaluated value according to an AE evaluated value acquired atthe time of flashing the strobe light. Therefore, the probability ofsaturation of AF evaluated values which is due to the position of thelens system 101 can be reduced.

With the present invention, in the apparatus described above, it isdetermined whether flashing is possible in the light quantity to beflashed required for the number of sampling times of an AF evaluatedvalue or not, and when it is determined that the flashing is notpossible, a strobe-light quantity to be flashed is reduced or the numberof sampling times of an AF evaluated value is reduced. Therefore, it canenhance the possibility of obtaining proper focus can be enhanced evenwith an electronic flash device having a limited function.

With the present invention, in the apparatus described above, an AEevaluated value acquired when a strobe light is flashed is compared toan AE evaluated value acquired without flashing a strobe light, and whenit is found that both of the values are not different, flashing is notmade for sampling an AF evaluated value. Therefore, it can prevent awaste of power consumption as well as of time for execution. Althoughthe invention has been described with respect to a specific embodimentfor a complete and clear disclosure, the appended claims are not to bethus limited but are to be construed as embodying all modifications andalternative constructions that may occur to one skilled in the art whichfairly fall within the basic teaching herein set forth.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

1. An autofocus apparatus comprising: an image pickup means forconverting light of an object received through a focus lens system toelectric signals and outputting the signals as image data; an A/Dconverting means for A/D-converting the image data to obtain digitalimage data; an AF evaluating means for outputting an AF evaluated valueobtained by integrating high-frequency components of brightness data inthe digital image data; a sampling means for sampling the AF evaluatedvalue obtained by said AF evaluating means while moving a position ofsaid focus lens system; a flash means for illuminating light; and afocus driving means for determining a focus according to a result of thesampling of the AF evaluated value by said sampling means and drivingsaid focus lens system to the focus position, wherein the illuminatinglight is flashed in synchronism with a sampling timing of the AFevaluated value.
 2. The autofocus apparatus according to claim 1,wherein the range where the AF evaluated value is sampled is set to arange where the light of the flash can reach.
 3. The autofocus apparatusaccording to claim 1, wherein the light of the flash is used to obtainthe AF evaluated value as well as for reducing red-eye effect.
 4. Theautofocus apparatus according to claim 1, further comprising: an AEevaluating means for calculating an AE evaluated value corresponding tothe brightness data in the digital image data, wherein a quantity of thelight of flash is determined in synchronism with the sampling timing ofthe AF evaluated value according to the AE evaluated value acquired atthe time of the flash.
 5. The autofocus apparatus according to claim 1,wherein it is determined whether or not a flash having a required lightquantity can be performed for a number of sampling times of the AFevaluated value, and when it is determined that the flash can not beperformed then the light quantity of the flash is reduced or the numberof sampling times of the AF evaluated value is reduced.
 6. The autofocus apparatus according to claim 1, further comprising: an AEevaluating means for calculating an AE evaluated value corresponding tothe brightness data for the digital image data, wherein the AE evaluatedvalue acquired when the flash is performed is compared to the AEevaluated value acquired without the flash, and when both of the valuesare not different, the flash is not performed when sampling the AFevaluated value.
 7. An autofocus apparatus, comprising: an image pickupdevice which converts light of an object received through a focus lenssystem to electric signals and outputting the signals as image data; anA/D converter which A/D-converts the image data to obtain digital imagedata; an AF evaluating unit which outputs an AF evaluated value obtainedby integrating high-frequency components of brightness data in thedigital image data; a sampling unit which samples the AF evaluated valueobtained by said AF evaluating unit while moving a position of saidfocus lens system; a flash which illuminates light; and a focus driverwhich determines a focus according to a result of the sampling of the AFevaluated value by said sampling unit and driving said focus lens systemto the focus position, wherein the illuminating light is flashed insynchronism with a sampling timing of the AF evaluated value.
 8. Theautofocus apparatus according to claim 7, wherein a range where the AFevaluated value is sampled is set to a range where the light of theflash can reach.
 9. The autofocus apparatus according to claim 7,wherein the light of the flash is used to obtain the AF evaluated valueas well as for reducing red-eye effect.
 10. The autofocus apparatusaccording to claim 7, further comprising: an AE evaluating unit whichcalculates an AE evaluated value corresponding to the brightness data inthe digital image data, wherein a quantity of the light of flash isdetermined in synchronism with the sampling timing of the AF evaluatedvalue according to the AE evaluated value acquired at the time of theflash.
 11. The autofocus apparatus according to claim 7, wherein it isdetermined whether or not a flash having a required light quantity canbe performed for a number of sampling times of the AF evaluated value,and when it is determined that the flash can not be performed then thelight quantity of the flash is reduced or the number of sampling timesof the AF evaluated value is reduced.
 12. The autofocus apparatusaccording to claim 7, further comprising: an AE evaluating unit whichcalculates an AE evaluated value corresponding to the brightness datafor the digital image data, wherein the AE evaluated value acquired whenthe flash is performed is compared to the AE evaluated value acquiredwithout the flash, and when both of the values are not different, theflash is not performed when sampling the AF evaluated value.